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, depending on the compiler and used optimization level, the compiler may interpret the conditional as always true (because func can be seen as undefined from a standards point of view). [7] An alternative to the above construct is using a system API to check if func is defined (e.g. dlsym with RTLD_DEFAULT). The above check may also fail for ...
This can result in bugs that are exposed when a different compiler, or different settings, are used. Testing or fuzzing with dynamic undefined behavior checks enabled, e.g., the Clang sanitizers, can help to catch undefined behavior not diagnosed by the compiler or static analyzers. [5] Undefined behavior can lead to security vulnerabilities in ...
This can be understood as taking a null pointer of type structure st, and then obtaining the address of member m within said structure. While this implementation works correctly in many compilers, it has generated some debate regarding whether this is undefined behavior according to the C standard, [2] since it appears to involve a dereference of a null pointer (although, according to the ...
GCC has been ported to more platforms and instruction set architectures than any other compiler, and is widely deployed as a tool in the development of both free and proprietary software. GCC is also available for many embedded systems, including ARM-based and Power ISA-based chips.
Although on GCC and LLVM this particular program compiles and runs as expected, more complicated examples may interact with assumptions made by strict aliasing and lead to unwanted behavior. The option -fno-strict-aliasing will ensure correct behavior of code using this form of type-punning, although using other forms of type punning is ...
However, GCC's nested functions, unlike blocks, must not be called after the containing scope has exited, as that would result in undefined behavior. GCC-style nested functions currently use dynamic creation of executable thunks on most architectures when taking the address of the nested function. On most architectures (including X86), these ...
However, more often it is taken to refer to the actual use of an entity before any declaration; that is, the first reference to second in the code above is a forward reference. [2] [3] Thus, we may say that because forward declarations are mandatory in Pascal, forward references are prohibited. An example of (valid) forward reference in C++:
It also means that, for example, the bitand keyword may be used to replace not only the bitwise-and operator but also the address-of operator, and it can even be used to specify reference types (e.g., int bitand ref = n). The ISO C specification makes allowance for these keywords as preprocessor macros in the header file iso646.h.